Effects of ampicillin on cystine/glutamate antiporter and glutamate transporter 1 isoforms as well as ethanol drinking in male P rats

Abstract

Evidence demonstrated that glial cells, mainly astrocytes, regulate glutamate uptake through several glutamate transporters. Among these glutamate transporters, glutamate transporter 1 (GLT-1; its human homolog is excitatory amino acid transporter-2) is responsible for the majority of glutamate uptake. Cystine-glutamate antiporter (xCT) is another glial protein critical in regulating glutamate transmission. Several studies from our laboratory demonstrated that attenuation of ethanol intkae was associated in part with upregulation of xCT and GLT-1 expression suggesting the important role of these transporters in the treatment of ethanol dependence. We found recently that β-lactam antibiotic, ampicillin, upregulated GLT-1 expression in the prefrontal cortex (PFC) and nucleus accumbens (NAc) and consequently reduced ethanol intake in alcohol-preferring (P) rats. In this study, we investigated the effects of ampicillin on the expression of xCT and GLT-1 isoforms (GLT-1a and GLT-1b) as well as on GLAST expression. We found that ampicillin reduced ethanol intake as compared to the saline (control)-treated group. In addition, we found that ampicillin induced upregulation of xCT, GLT-1a, and GLT-1b expression in both the PFC and NAc, but had no effect on GLAST expression. Our findings provide significant role of ampicillin on upregulating xCT and GLT-1 isoforms expression, might be suggested as possible targets for the attenuation of ethanol consumption.

Keywords: Ampicillin; Ethanol intake; GLAST; GLT-1a; GLT-1b; Glutamate; xCT.

Figure 1

Effects of ampicillin treatment on ethanol and water intake (g/kg/day) in male P rats exposed to five weeks of continuous free choice of ethanol and water Significant difference between treatment groups. A) Effects of ampicillin treatment on ethanol intake (g/kg/day). B) Effects of ampicillin treatment on water intake (g/kg/day). Data are shown as mean ± SEM; (n= 6 for each group), (*p<0.05; #P<0.0001)

Figure 2. Effect of ampicillin on GLT-1a expression in NAc and PFC

A) Immunoblots for GLT-1a expression and GAPDH as a control loading protein in the NAc and PFC. B) Quantitative t-test analysis of immunoblots showed that ampicillin increased significantly the % ratio of GLT-1a/GAPDH in the NAc and PFC as compared to the saline/control group (100% control-value). Data are shown as mean ± SEM. (*p<0.05). (n= 6 for each group)

Figure 3. Effect of ampicillin on GLT-1b expression in NAc and PFC

A) Immunoblots for GLT-1b expression and GAPDH as a control loading protein in the NAc and PFC. B) Quantitative t-test analysis of immunoblots revealed that ampicillin increased the % ratio of GLT-1b/GAPDH significantly in the NAc and PFC as compared to the control group (100% control-value). Data are shown as mean ± SEM. (*p<0.05). (n= 6 for each group)

Figure 4. Effect of ampicillin on xCT expression in NAc and PFC

A) Immunoblots for xCT expression and GAPDH as a control loading protein in the NAc and PFC. B) Quantitative t-test analysis of immunoblots showed that ampicillin increased the expressions of the % ratio of xCT/GAPDH in the NAc and PFC significantly as compared to the control group (100% control-value). Data are shown as mean ± SEM. (*p<0.05). (n= 6 for each group)

Figure 5. Effect of ampicillin on GLAST expression in NAc and PFC

A) Immunoblots for GLAST expression and GAPDH as a control loading protein in the NAc and PFC. B) Quantitative t-test analysis of immunoblots showed no significant increase in the % ratio GLAST/GAPDH in the NAc and PFC of either the control group (100% control-value) or the treatment group. Data are shown as mean ± SEM. (*p<0.05). (n= 6 for each group)